ADSORPTION OF N-ALKANES ON CARBON-FIBERS AT ZERO SURFACE COVERAGE

The Henry's law region of the adsorption isotherms for a series of n-alkanes (C//8-C//1//3) on two types of carbon fibers was studied by inverse gas chromatography. The heat, entropy, and free energy of adsorption, calculated from retention data, vary linearly with the number of carbon atoms. The low heats of adsorption for both high-modulus and high-strength fibers indicate a virtual absence of high-energy sites. Increased values of heats of adsorption obtained after the cleaning of the fibers for 100 h in nitrogen at 160 degree C suggest that the high-energy sites on 'as received' fibers are occupied by physically adsorbed species (CO//2, H//2O). It is shown that the entropy loss upon adsorption cannot be attributed solely to the loss of one degree of translational freedom and that contributions from rotational and conformational entropy losses must be taken into account.